Magnetic motion transducer



y 17, 1956 J. s. HICKEY, JR 2,755,403

MAGNETIC MOTION TRANSDUCER Filed Oct. 22. 1952 Fig.1.

Inventor": John S. HickegJn His Attorney.

:MAGNETIC MOTION TRANSDUCER 101m S.'Hickey, JL, 'Cohoes, N. Y., assignor to General Electric .Company, .a corporation .of New York Application October 22, 1952, Serial No. 316,251

Claims. (Cl. 313-72) The invention relates to magnetic motion transducers.

For producing electrical signals responsive in amplitude to small mechanical movements, the discharge current of an evacuated discharge device may be directly cont-rolled. This is achieved in some prior art transducers by moving one'of the device elements through a diaphragm or similar means. It is desirable, however, to provide a simplified discharge device structure utilizing more or less standard components and techniques developed for low cost mass production vacuum tubes, while providing very high sensitivity.

It is an object of my invention to provide an improved motion transducer incorporating a magnetically controlled electron discharge device.

:It is a further object of my invention to provide an electron discharge device for a magnetic motion transducer requiring no moving parts in vacuum.

it is a still further object of my invention to provide a simplified and low cost beam-type discharge device for prodpcing a collectionrcurrent responsive to the magnitude of an externally imposed magnetic field.

Briefly, in accordance with one aspect of my invention I an evacuated discharge device having an electron beam forming and collecting system is provided with a pair .of pole pieces made of magnetic material positioned along -a portion of the beam path on either side of it. A change in an external magnetic field, such as caused by the motion or displacement of a magnet outside of the discharge device, affects its magnetic coupling to the in- :ternal pole pieces, and thus varies the deflection of the electron beam. The resulting beam displacement provides a collector current change which very sensitively reflects the ampliude of the magnet motion. in a particular embodiment illustrated, a discharge device is provided with an envelope made -of magnetic material which must be saturated by the field of the magnet before any useful field is attained between the internal pole pieces, whereby the sensitivity of the transducer is enhanced.

The novel features which are considered to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing wherein:

Fig. l is an exploded view of'the elements of a transducer embodying my invention, and

Figs. 2 and 3 are front and side views respectively of a specific discharge device arranged according to my invention.

Referring now to Fig. 1, an exploded view of a discharge device ,1 is represented minus the device envelope for purposes of illustrating the transducer construction and operation. A cathode 2 provides the electron discharge, the cathode suitably being of the sleeve type havingan internal heater. Conventional control electrodes 3 and 4 of non-magnetic material, for focusing and accelerating the electron beam are spaced from the cathode.

2,755,403 Patented .July 17, 1956 For purpose, the electrodes 3 and 4 have respective openings ;or windows 5 and 6, the windows being aligned to restrict and direct the electron beam. The electron beam then passes between apair of magnetic pole pieces 7 and 8 which are designed to provide a magnetic field between them perpendicular to the direction of the electron beam. A suitable split anode arrangement, such as a pair of anodes or collector electrodes 9 and 10 of non-magnetic material, collects the electron beam current, the current being divided between them according to the displacement of the beam by the magnetic field between the pole pieces 7 and 8. As shown in Fig. '1, the collection surface of the anode -9 is arranged in the path of the undeflected beam, the second anode 10 being snitably positioned in front of a portion of the anode 9 to collect the-electrons which have been su'fiiciently deflected in that direction by the magnetic field. As is well understood, the direction of deflection is perpendicular to both the magnetic field and the electron path.

7 The motion or displacement desired to be measured or detected is transmitted to a permanent magnet 11 which is positioned outside of the discharge device 1. A rod '12 or' any other suitable actuating means has one end fixed to the magnet and the other end suitably coupled to the source .of the movement. The respective poles 13 and 14 of the magnet are aligned to be respectively adjacent but spaced from the ends of the internal pole pieces 7 and 8. Any change in the amount of magnetic coupling between the magnet 11 and the pole pieces 7 and 8 affects the magnetic field between the pole pieces which in turn controls the amplitude of the electron stream. In the construction of Fig. 1, the magnetic system is arranged to provide maximum sensitivity when the displacement results in a linear movement of the magnet 11 to or from the pole pieces to change the length of the air gap. Ac cordingly, the ends of the pole pieces '7 and 8 are respectively bent over to provide relatively large surfaces approximately coextensive with the eifective pole surfaces of the magnet 11. It is to be understood, of course, that magnetic coupling may be varied by angular movement of the activating rod 12 or as otherwise desired.

In operation, the heater of cathode Z is connected to a suitable source of heater current conventionally represented as a battery 15 and the control electrodes 3 and 4 are provided with a positive potential with respect to the cathode to accelerate the electrons and provide the desired beam focusing action. Accordingly, the electrode 3 is provided with a positive potential with respect to the cathode by a battery 16 and the electrode 4 is given a more positive potential by a battery 17 connected between it and the electrode 3. The electrode 4 is conductively supported between the pole pieces 7 and 8, thus also placing the pole pieces at a positive potential. This composite structure thus provides both electric and magnetic field control of the electron beam.

The anodes 9 and 10 are also provided with a positive potential, which may suitably be that of the second control electrode 4 and are respectively connected through load resistors 18 and 19 to the electrode 4. When the collected beam current is not equally divided between the anodes a voltage difference will be maintained between them due to the different voltage drops across their respective load resistors 18 and 19. This voltage is suitably presented to terminals 26 and 21 which are connected respectively to the anodes 9 and 10. Thus, it may be seen that a change'in the magnetic field between the pole pieces 7 and 8 results .in either more or less deflection of the electron beam, hence resulting in more or less electron current deflection between the two electron collecting anodes. The signal appearing between the terminals 20 and 21 is suitably employed as desired, such as in an electrically responsive indicator or feedback circuit. If desired, the current or voltage at only one of the anodes may be utilized as the output signal.

Referring now to Figs. 2 and 3 front and side views respectively of a discharge device corresponding to the device 1 shown in exploded view of Fig. 1 are presented. As may be seen, the elements previously referred to, namely the cathode 2, first control electrode 3, second control electrode 4, pole pieces 7 and 8 and anodes 9 and 10 are supported between top and bottom mica spacers 22 and 23. This electrode assembly is enclosed within a tubular envelope 24 preferably made of steel or other magnetic material. The reason for having an envelope of magnetic material is explained in a following paragraph. The bent-up ends of the pole pieces 7 and 8 extend beyond the top mica 22 and are adjacent but slightly spaced from the upper end of the envelope. This spacing is maintained by a thin mica spacer member 25. The electrodes are connected by supporting leads below the bottom spacer 23 to leads 26 which are sealed through the lower end or stem of the envelope, a suitable base assembly 27 including base pins being provided for external connections.

The device is suitably evacuated and a getter 28 may also be employed in a conventional manner to clean up any residual gases. As may be seen from inspection of Figs. 2 and 3 the construction of the device is relatively simple and corresponds closely to that developed for low cost discharge device types adapted for mass production. The magnet 11, as previously stated, is not part of the discharge device and it is obvious that the device may be used to measure changes in magnetic fields however produced. While the motion of the entire discharge device with respect to a magnet may be the subject of measurement, the pole pieces 7 and 8 inside the device envelope are themselves fixed in position.

To provide maximum transducer sensitivity the envelope is designed to be a saturable magnetic shunt in the field of the magnet 11. This follows from the fact that a certain minimum spacing is required between the pole pieces 7 and 8 in order that the electron beam may pass between them. To reduce the flux density between them, another gap must be added in the magnetic circuit, the additional gap being the sum of the gaps between the pole pieces and the magnet poles. Were it not for the magnetic material of the envelope, the total air gap of the magnetic circuit would have to be doubled in order to reduce the flux between the pole pieces by one half. Accordingly, in order to provide a large change of the flux controlling the anode voltage differential, for magnet displacements which are small with respect to the pole piece spacing, the envelope is of a magnetic material which must be saturated before any useful flux is available within the envelope. After saturation, however, no further flux is shunted through the envelope and a very small change in the air gap produces a relatively large change in the magnetomotive force between the pole pieces. The overall etfect is the same as if the motion to be measured were amplified by a mechanical linkage so as to be large with respect to the pole piece spacing.

While the present invention has been described by reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is: a

1. A transducer for providing an electrical signal related in amplitude to the position of a magnet comprising a discharge device having an envelope at least a portion of which is made of magnetic material, means for producing an electron beam along a path, an anode, and a pair of pole pieces made of magnetic material positioned on opposite sides of said path and including mag netic coupling portions closely spaced to said magnetic envelope portions.

2. An electron discharge device having an evacuated envelope having a portion of magnetic material and containing an electron gun for forming an electron beam, collector electrodes interposed across the beam path for dividing the electron collection current according to the beam deflection, and a pair of magnetic pole pieces for providing a magnetic deflecting field made of magnetic material and positioned on opposite sides of the beam path, said pole pieces having coupling portions thereof adjacent the inner wall of the envelope and an external magnet movably positioned externally of said envelope and magnetically coupled to said coupling portions of said pole pieces through said magnetic portion of said envelope.

3. An electron discharge device comprising a tubular envelope having a closed top portion made of a saturable magnetic material, top and bottom spacer members transversely positioned within said envelope, and a plurality of electrodes positioned between said spacer members comprising an electron emissive cathode, an accelerating electrode made of a non-magnetic material, said accelerating electrode having an aperture therethrough for defining an electron beam path, a pair of pole pieces made of magnetic material for deflecting said beam positioned on either side of the electron beam path each having an end portion closely spaced from said magnetic top portion and conductively engaged by said accelerating electrode, and collector electrodes supported in spaced relation in the direction of beam deflection for dividing the beam currents according to the beam deflection introduced by any magnetic field between the pole pieces.

4. A magnetic displacement transducer comprising an electron discharge device having a tubular envelope with a closed top portion made of a saturable magnetic material, an external magnet having its poles slightly spaced from said envelope top portion to saturate said top portion and in a position corresponding to a displacement to be measured, top and bottom spacer members transversely positioned within said envelope, and a plurality of electrodes positioned between said spacer members comprising an electron emissive cathode, an accelerating electrode made of a non-magnetic material, said accelerating electrode having an aperture therethrough for defining an electron beam, a pair of pole pieces made of magnetic material positioned on either side of the electron beam path, each of said pole pieces having an end portion extending above the top spacer member closely spaced from said magnetic top portion for focussing between them the magnetic field in excess of that utilized to saturate said top portion, said pole pieces conductively engaging said accelerating electrode, and collector electrodes supported in spaced relation in the direction of beam deflection for dividing the beam currents according to the beam deflection varying with the magnetic field between the pole pieces.

5. A transducer for producing an electric signal related in amplitude to the position of a magnet comprising a discharge device having a generally planar end portion of magnetic material, means within the envelope for producing an electron beam along a path, an anode and a pair of pole pieces positioned on opposite sides of said path and including magnetic coupling portions closely spaced and parallel to said generally planar end portion of magnetic material.

References Cited in the file of this patent UNITED STATES PATENTS 1,882,449 Ruben a Oct. 11, 1932 2,067,817 Beggs Jan. 12, 1937 2,165,307 Skellett July Il, 1939 2,352,657 Potts July 4, 1944 

